Unsteady-state Directional Solidification Of A Hypoperitectic Pb-9.5wt%bi Alloy

Although considerable attention has been paid to studies on the unidirectional solidification of peritectic alloys, most of these investigations are carried out under steady-state solidification, where both the growth rate and the thermal gradient can be independently controlled and held constant in time. In this work, a hypoperitectic Pb-9.5wt%Bi alloy was directionally solidified under unsteady-state heat flow conditions and the microstructure evolution was analyzed. Continuous temperature measurements in the casting were monitored during solidification, using a data acquisition system and a bank of six type J thermocouples positioned along the casting length. Thermal parameters such as the growth rate (v) and the cooling rate (Ṫ) were experimentally determined by the experimental cooling curves. The solidification microstructure was characterized by a dendritic morphology along the entire casting length. The primary (λ1) and secondary (λ2) dendrite arm spacings were measured and experimental growth laws relating them to the solidification thermal parameters v and Ṫ are proposed. © (2013) Trans Tech Publications, Switzerland.730-732889894 Portuguese Materials Society- SPM,School of Engineering of the University of Minho,CT2M - Centre for Mechanical and Materials Technologies,Institute for Polymers and Composites/I3N,3B's Res. Group on Biomater., Biodegradables and BiomimeticsNassar, H., Fredriksson, H., On peritectic reactions and transformations in low-alloy steels (2010) Metall. Mater. Trans. A, 41, pp. 2776-2783Su, Y., Liu, D., Li, X., Luo, L., Guo, J., Fu, H., Preparation of the initial solid-liquid interface and melt in directional solidification of Al-18 at%Ni peritectic alloy (2010) J. Cryst. 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Steady And Unsteady State Peritectic Solidification

In the present study, PbBi as a model of alloys from peritectic systems was directionally solidified under transient heat flow conditions, which is the class of heat flow encompassing the majority of industrial solidification processes. Some experiments were also carried out in a vertical tube furnace under cooling rates closer to equilibrium during solidification in order to broaden the range of solidification parameters. Thermal parameters such as the tip growth rate (VL) and the cooling rate (T) were experimentally determined and correlated with the primary (λ1) and secondary (λ2) dendrite arm spacings by experimental growth laws. It is shown that the proposed growth laws are able to encompass also the growth of dendritic branches during steady state growth from the melt.311105114Nassar, H., Fredriksson, H., On peritectic reactions and transformations in low-alloy steels (2010) Metall. Mater. Trans. 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Thermal Parameters and Microstructural Development in Directionally Solidified Zn-Rich Zn-Mg Alloys

Transient directional solidification experiments have been carried out with Zn-Mg hypoeutectic alloys under an extensive range of cooling rates with a view to analyzing the evolution of microstructure. It is shown that the microstructure is formed by a Zn-rich matrix of different morphologies and competitive eutectic mixtures (Zn-ZnMg and Zn-ZnMg). For 0.3 wt-pct Mg and 0.5 wt-pct Mg alloys, the Zn-rich matrix is shown to be characterized by high-cooling rates plate-like cells (cooling rates >9.5 and 24 K/s, respectively), followed by a granular–dendritic morphological transition for lower cooling rates. In contrast, a directionally solidified Zn1.2 wt-pct Mg alloy casting is shown to have the Zn-rich matrix formed only by dendritic equiaxed grains. Experimental growth laws are proposed relating the plate-like cellular interphase, the secondary dendritic arm spacing, and the eutectic interphase spacings to solidification thermal parameters, i.e., cooling rate and growth rate. The experimental law for the growth of secondary dendritic spacings under unsteady-state solidifications is also shown to encompass results of hypoeutectic Zn-Mg alloys subjected to steady-state Bridgman growth.The authors acknowledge the financial support provided by FAPESP-São Paulo Research Foundation, Brazil (Grants 2012/08494-0, 2013/15478-3, 2013/25452-1, 2013/23396-7, 2014/50502-5), CNPq-The Brazilian Research Council, and CSIC-Spanish National Research Council (Project i-link0944).Peer Reviewe